EQ is shorthand for equatorial, and the numbers attached to it, EQ3, EQ5, EQ6 and the rest, are a size ladder rather than a set of features. Reading that ladder correctly is most of what you need to buy one sensibly.
What the numbers mean
They indicate load capacity and mass. A small EQ carries a light refractor and wobbles under anything more; a large one carries a 200mm reflector and a camera. The published capacity is usually optimistic for imaging: a common rule among imagers is to load a mount to no more than about half its stated visual capacity.
What a German equatorial looks like
The tube sits on one end of a shaft with counterweights on the other, and the whole assembly turns about an axis pointed at the celestial pole. That gives excellent balance and one quirk: crossing the meridian requires flipping the mount to the other side of the pier, which interrupts imaging and confuses every beginner once.
Setting one up
Level the tripod, set the latitude scale to your own, point the polar axis north, balance the tube in both axes with the counterweights, then polar align to whatever accuracy your use needs. Ten minutes the first few times and five afterwards, and skipping the balance step is what makes motors strain and tracking wander.
Whether you need one
For visual observing, no: an alt-azimuth or dobsonian mount is steadier per pound and needs no setup. For long exposure imaging, effectively yes. The EQ mount exists to make tracking mechanically simple, and if you are not integrating exposures you are paying for something you will not use.
Questions people ask about eq mount
What is an EQ mount?
An equatorial mount, usually the German pattern with a counterweighted shaft, whose main axis points at the celestial pole so one motion follows the sky.
What do EQ3, EQ5 and EQ6 mean?
A size and capacity ladder. Larger numbers carry heavier instruments; for imaging, load to about half the stated visual capacity.
Do I need an equatorial mount for visual observing?
No. A dobsonian or alt-azimuth mount is steadier for the money and needs no alignment. The EQ earns its price when exposures get long.